Method of coating metal



June 10, 1941.

R. F. RENKIN METHOD OF COATING METAL Filed Jan. 25, 1940 Patented June10, 1941 2,245,226 Marnon or COATING METAL Robert F. Rankin. Sharon, Pa.Application January 23, 1940, Serial No. 315,185

18 Claims.

' The invention relates generally to the coating of metal products, andmore particularly to the galvanizing of steel sheets, stripsheets,strips or wire, and this application is a continuation in part of mycopending' application Serial No. 309,224, flied December 14, 1939 Thepresent method preferably includes as one step the cleaning of steel inpreparation for coating by means oi? a so-called dry pickle treatmentinstead of the usual wet pickle in an acid bath. Said "dry pickletreatment .per se is not part of this invention and may be describedpreferably as including passing the steel through a heated controlledactive atmosphere adapted for carrying oil scale and other surfaceimpurities in the form of gases or vapors.

For zinc coating or galvanizing certain kinds of steel, a relativelysatisfactory galvanized coating can be obtained by passing the steelfrom a usual cleaning step directly into the spelter pot. However, thecoating on the coated product thus obtained may not be suflicientlyductile or adherent for certain purposes,- and it straight zinc spelteris used the coating powders or flakes off under forming operations.

Moreover, when the carbon content of the steel being coated issubstantially below about 0.1%, it becomes increasingly diiiicult toobtain a galvanized coating which is ductile and adherent.

Where it is desired to galvanize steel having a very low carbon content,as for instance steel telephone wire requiring .02% or .03% carbon aswell as a low phosphorus and -a low sulphur content, the paming of thesteel directly into the spelter pot gives a very poor coating which, haslittle adhesion and flakes ofl very readily, es-

pecially when the standard test of twisting the wire around its owndiameter is applied.

I have discovered that, .by passing the steel product directly from thedry pickle cleaning treatment through a special liquid flux and thenthrough a galvanizing bath containing a small amount oi aluminum, thecoating obtained is very adhesive and ductile, and does not flake whensubjected to thestandard twisting test.

A general object oi the present invention is to provide a novel andimproved method of galvanizing metal.

A more specific object is to provide a method of galvanizing steelhaving a low carbon content.

Another specific object is to provide an improved method of coatingsteel telephone wire with a ductile and. adhesive galvanized coating.

A further object is to provide a novel and imgalvanizing step forforming a uniform him onthe steel product priorto the coating treatment.

A still further object is to provide a special galvanizing bath forforming a ductile and adhesive coating on the steel product after itpasses through the special fluxing bath.

These and other objects are accomplished by the improvements, methods,combinations and sub-combinations comprising the present invention, apreferred embodiment of which is hereinafter described in detail anddefined in the appended claims.

In general terms the invention may be defined as including the steps ofpassing a steel sheet. strip or wire product through a preheating zone,then through a dry pickling or cleaning zone, then through a liquid fluxof zinc ammonium chloride with nickelous chloride, and then through agalvanizing bath of pure zinc spelter with a small percentage ofaluminum.

In the drawing I have shown by way of example a diagrammaticrepresentation of apparatus adapted for the continuous coating of steelwire, but it will be understood that the apparatus can be greatly variedwith respect to construction and arrangement and the material beingcoated can be steel ,strip or steel sheets or various other products,without departing from thescope of the invention as defined in theclaims. 7

In the drawing- Figure 1 is a diagrammatic plan view of a preferredembodiment of apparatus for carrying out the present improved method;and

Fig. 2 is a diagrammatic side elevation thereof partly in section.

Like reference characters refer to like parts throughout the drawing. I

In continuously coating steel wire the strands of wire 9 may bepulled'from pay off reels I! over a feed roll II and welder l2, all in ausual manner, and thence through a preheating furnace indicated at it,which is maintained preferably at a temperature of about 1000 F.

An example of wire 9 treated maybe steel telephone wire or No. 101 wirehaving an approximate analysis of .03 carbon, .10 manganese, .029

' sulphur, .008 phosphorus, and no silicon addiistics, and it isexceedingly dimcult if not substantially impossible to obtain asufficiently ductile and adherent galvanized coating on such wire byusing any of the conventional coatingprocesses in commercial use.

The wire 9 passes from the preheating furnace tains preferably air,natural gas, and chlorine in certain definite proportions, as forexample the air may be passed through the munle at the rate of 42 cubicfeet per hour, the natural gas at 7 cubic feet per hour and the chlorineat 7 cubic feetper hour, said proportions being dependent upon thecapacity of the furnace.

The construction of the dry pickling apparatus and the method ofcleaning per se which is performed thereby is not in itself a part ofthis invention, except that the cleaning step is an important step inthe combination of steps constituting the method of the presentinvention.

It is deemed suflicient to say that the wire strands entering the muflieIS in the dry pickling furnace l5 may have on their surface the usualiron oxide scale, and also other impurities and foreign matter such asoil, rust, dirt, lime, grease, and carbon: and the effect of the gastreatment atthe particular furnace temperatures maintained is tochemically react with and gasify or vaporize substantially all of theseimpurities. The impurities are carried off as gases or entrained in thegases so that the wire strands emerge from the furnace IS with a cleansurface except for a slight uneven film of chemical salts.

This salt film is uneven and spotty, and if the wire is passed directlyfrom the furnace l5 into a galvanizing pot', the coating is notuniformly ductile nor suiliciently adherent, but will flake off when thewire is tested by twisting or coiling it about its own diameter. Theflaking off of the coating apparently occurs at the places where thespots or accumulations of the salt film are located when the wireemerges from the dry pickling furnace.

Passing the wire through the usual flux of zinc chloride before the wireenters the spelter does not satisfactorily eliminate this flakingdifficulty, but I have found that if the wire is passed directly fromthe dry pickling furnace l5 through a separate flux bath of specialcomposition, and

then through'a galvanizing bathic'f substantially pure zinc with a smalladdition of aluminum, the resulting coating is uniformly ductile andvery adherent so .as not to flake oif when tested by twisting it aboutits own diameter.

Accordingly, the wire strands leaving the furnace ii are passed throughthe depending portion I6 01' the muliie directly into a separate fluxbath i1 and around hold down rolls il' therein. The composition of theflux bath I1 is a solution of zinc ammonium chloride containing about0.5% to 1.0% of nickelous chloride or 0.5% to 1.0% aluminum chloride, orpreferably 0.5% to 1.0% of each, forming a flux with a Baum reading ofabout 25 at about 160 F., which is constantly being filtered, therebyremoving all im- I 2,246,226 the required electrical properties andcharacter purities and maintaining a good, clean flux at all times.

The effect produced by the presence of nickelous chloride and aluminumchloride in the flux is not clearly understood, but they appear touniformly spread or distribute the salt film over the surface of thewire, and the aluminum chloride also improves the flow in thegalvanizing bath, and the coating is uniformly adherent and does notflake off when twisted.

From the flux bath I! the wire strands are led over suitable exit andentry rolls l9 into a galvanizing bath 20, and in the galvanizing baththe strands pass under hold down rolls 2!, and then upward through apalm oil and charcoal wipe 22 or other conventional wipe, and over apull-over roll 23 and tension rolls 24 to the take up reels indicatedgenerally at 25.

The galvanizing bath 20 is preferably made up entirely of a high gradespelter which is zinc having a very low content of impurities with anaddition of from 06% to .1% of aluminum, and the bath is maintained at atemperature of approximately 800" to "840 F. The addition of aluminum tothe galvanizing bath improves the coating obtained by breaking downsurface tension, and by giving a better color and flow to the coating,as well as rendering it more ductile.

The present method is particularly adapted to the use of aluminum in thespelter, because the 'flux is in a bath separate from the galvanizingbath. Where the flux is located on the galvanizing bath the presence ofaluminum inthe spelter has a deleterious effect in that it produces ablack scum at the surface of the bath and deadens the flux.

I have found by actual experiment that the method of this invention willproduce a much better galvanized coating on ordinary strip steel thancan be produced by the conventional method of wet pickling with acid andthen coating in the usual galvanizing pot, and that the improvement inthe coating becomes more pronounced when the carbon content of the steelapproaches .05% or under.

Also by this method I am able to produce a coated steel product giving avery low Rockwell and a high Olsen test. I believe that these unusualresults are due largely to the impossibility of the occurrence of anyhydrogen absorption, causing embrittlement, which condition is always ahazard when the steel is treated in a conventional manner by wetpickling.

An example of a steel product coated by this method wherein the steel issoft and the coating ductile is as follows: low carbon (under .09%)strip steel .014" thick has been coated according to this method andthen rolled to .003" thick, and still retains a uniform and ductilecoating which will not flake or powder when bent flat on itself.

These results are substantially duplicated in galvanizing wire, andwhere the wire has an analysis of the order of 101 telephone wire, asfor example .03% carbon, .10% manganese, 029% sulphur, and .008%phosphorus, a coating obtained by the method of this invention is farmore uniform, ductile and adherent than it has been heretofore possibleto obtain by known commercial methods of galvanizing.

Although the galvanized coating produced on metal products, by firstpassing them through the special flux herein described and then throughthe spelter, is better in every way than can be produced by priormethods, I have found that the coating is still more improved byelectrolyzing the flux bath with the metal acting as the anode,

This may be done as diagrammatically .indicated in Fig. 1, wherein apower source of direct current is represented by the motor generator",the positive side of which is connected by conductor 21 to one of theholddown rolls l8, and the negative side being connected by theconductor 28 to the flux; tank 29.

Accordingly electric current flows from the wire strands 9, which aremade the anode in the flux tank, through the flux bath I! to the fluxtank acting as the cathode, and the consequent electrolyzing of the fluxbath appears to augment and.

accelerate the action of the flux on the wire. The result is that thewire is cleaned better in the fluxing bath by throwing of! allimpurities due to the electric current'and at the same time beingfluxed, and after the wire is passed through.

the galvanizing bath 2!), the coating obtained is even more uniform,ductile and adherent than that produced when the flux is notelectrolyzed.

I claim:

1. A method of coating ferrous metal which.

includes subjecting the metal to a dry pickling treatment, pass ng themetal through a separate liquid flux solution of zinc ammonium chloridecontaining nickelous chloride, electrolyzing the flux during the passageof the metal therethrough by passing an electric current through theflux with the metal acting as the anode, and then passing the metalthrough a molten galvanizing bath of pure zinc containing a smallamountof aluminum.

2. A method of coating ferrous metal which includes subjecting the metalto a dry pickling treatment, passing the metal through a separate liquidflux solution of zinc ammonium chloride containing aluminum chloride,electrolyzing the flux during the passage of the metal therethrough bypassing an electriccurrent through the flux with the metal acting as theanode, and then passing the metal through a molten'galvanizing bath ofpure zinc containingv a small amount of aluminum.

4. A method of coating ferrous metal which includes subjecting the metalto a dry pickling treatment, passing the metal through a separate liquidflux solution of zincammonium chloride containing approximately from0.5% to 1.0% nickelous chloride, electrolyzing the flux duringthepassage of the metal therethrough by pasdng an electric currentthrough the flux with the metal acting as the anode, and then passingthe metal through a molten galvanizing bath of pure zinc containing from.06% to .l% aluminum.

5. A method ofcoating steel which includes preheating the steel to about1000 F., subjecting the steel to a heated controlled active atmospherecontaining chlorine, passing the steel through a separate liquid fluxsolution of zinc ammonium chloride containing nickelous chloride,electrolyzing the flux during the passage of the steel therethrough bypassing an electric current through the flux with the steel acting asthe "anode, and then passing the steel through a molten galvanizing bathof pure zinc with an addition of aluminum and maintained at anapproximate temperature of from -'=00 F. to 840 F.

6. A method of coating steel which includes preheating the steel toabout 1000 F., subjecting the steel to a heated controlled activeatmosphere containing chlorine, passing the steel through aseparate-liquid flux solution of zinc ammonium chloride containing 0.5%to 1.0% nickelous chloride and 0.5% to 1.0% aluminum chloride,electrolyzing the flux during the passage of the steel therethrough bypassing an electric current through the .flux with the steel acting asthe anode, and then passing the steel through a molten galvanizing bathof pure zinc with an addition of from .06% to .1% aluminum andmaintained at an approximate temperature of from 800 F. to 840 F.

'7. A method of coating ferrous strip, sheets or wire of low carboncontent and low metalloid content which includes preheating the ferrousproduct, subjecting the ferrous product to .a heated controlled activeatmosphere containing chlorine, passing the ferrous product through aseparate liquid flux solutionof zinc ammonium chloride containingnickelous chloride, electrolyzing the flux during the passage of theferrous product therethrough by passing an electric current through theflux with the ferrous product acting as the anode, and then passing theproduct through a molten galvanizing bath of substantially pure zinc.

8. A method of coating ferrous strip, sheets or wire of low carboncontent which includes subjecting the ferrous product to a heatedcontrolled active atmosphere containing chlorine, passing the ferrousproduct through a separate liquid flux solution of zinc ammoniumchloride containing nickelous chloride and aluminum 1.0% nickelouschloride, electrolyzing the flux.

during the passage of the ferrous product therethrough byelectriccurrent through the flux with the ferrous product acting as the anode,and then passing the product through a molten galvanizing bath of purezinc containing from .06% to .l% aluminum.

10. A method of coating ferrous strip, sheets or wire which includes thesteps of passing a cleaned ferrousproduct through a separate liquid fluxsohition of zinc ammonium chloride containing nickelous chloride,electrolyzing the flux during the passage of the. ferrous product 11. Amethod of coating ferrous strip, sheets or wire which includes the stepsof passing a cleaned ferrous product through a separate liduid fluxsolution of zinc ammonium chloride containing nickelous chloride andaluminum chloride. electrolyzing the flux during the passage of theferrous product therethrough by passing an electric current through theflux with the ferrous product acting as the anode, and then passing theproduct through a molten galvanizing bath.

12. A: method of coating ferrous strip, sheets or wire which includesthe steps of passing a cleaned ferrous product through a separate liquidflux solution of zinc ammonium chloride containing aluminum chloride,electrolyzing the flux during the passage of the ferrous producttherethrough by passing an electric current through the flux with theferrous product acting as the anode, and then passing the product"through a molten galvanizing bath.

13. In a method of coating steel of minimum carbon content, the steps ofpassing the cleaned steel through a separate liquid flux solution ofzinc ammonium chloride containing nickelous chloride and aluminumchloride, electrolyzing the flux during the passage of the steeltherethrough by passing an electric current through the flux with thesteel acting as the anode, and then passing the steel through a moltengalvanizing bath containing an aluminum addition. v

14. In a method of coating steel having a metallic salt film thereonresulting from dry pickling, the steps oi passing the steel through aseparate liquid flux solution of zinc ammonium chloride containingnickelous chloride, electrolysing the flux during the passage of thesteel therethrough by passing an electric current through the flux withthe steel acting as the anode, and then passing the steel through amolten bath of pure zinc containing a small amount of alumin;

15. A method of coating ferrous metal which includes the steps ofpassing the metal through a separate liquid flux solution of dncammonium chloride containing nickelous chloride, electrolys- 1118 theflux during thee of the metal therethrough bypassing an electric currentthrough the flux with the metal acting as the anode, and then passingthe metal'through a molten galvanizing bath of substantially pure zinc.

16. A method of preparing ierrous metal for coating which includessubjecting the metal to a dry pickling treatment, passing the metalthrough a separate flux solution of zinc ammonium chloride containingnickelous chloride, and electrolyalng the flun during the passage 'ofthe metal therethroughby passing an electric current through thefluxwith the metal acting as the anode.

17. A method of preparing ferrous metal for coating which includessubjecting the metal to a dry pickling treatment, passing the metalthrough a separate flux solution of zinc ammonium chloride containingnickelous chloride and aluminum chloride, and electrolyzing the fluxduring the passage of the metal therethrough by passing an electriccurrent through the flux with the metal acting as the anode.

18. A method of preparing ferrous metal for coating which includessubjecting the metal to a dry pickling treatment, passing the metalthrough a separate flux solution of zinc ammonium chloride containingaluminum chloride, and electrolyzing the flux during the passage of themetal therethrough by passing an electric current through the fluxwith'the metal acting as the anode.

nonm'r F. RE.

